The present invention relates to the techniques of chemical vapor infiltration that are used in particular when making parts out of thermostructural composite material. The invention relates more particularly to densifying porous substrates of complex three-dimensional shape such as fiber preforms for use in fabricating aeroengine blades, the substrates being densified by depositing a matrix therein.
In order to fabricate parts out of composite material, and in particular parts made of thermostructural composite material constituted by a refractory fiber preform (using carbon or ceramic fibers, for example) that is densified by a refractory matrix (e.g. made of carbon and/or ceramic), it is common practice to use chemical vapor infiltration methods. Examples of such parts are thruster nozzles made of carbon-carbon (C—C) composite, brake disks, in particular for airplane brakes, made of C—C composites, or blades made of ceramic matrix composites (CMCs).
Densifying porous substrates by means of chemical vapor infiltration consists in placing the substrates in a reaction chamber of an infiltration installation by using support tooling, and then in admitting a reagent gas into the chamber, with one or more ingredients of the reagent gas being precursors of the material that is to be deposited within the substrates in order to densify them. Infiltration conditions, and in particular the composition and the flow rate of the reagent gas, and also the temperature and the pressure inside the chamber, are selected so as to enable the gas to diffuse within the accessible internal pores of the substrates so as to deposit the desired material therein, as a result of one of the ingredients of the gas decomposing, or of a reaction taking place between a plurality of its ingredients. It is common practice for the reagent gas to be preheated by passing the gas through a preheating zone situated in the reaction chamber and into which the reaction gas inlet opens out. That method corresponds to the free-flow chemical vapor infiltration method.
In an industrial installation for chemical vapor infiltration, it is common practice to load the reaction chamber with a plurality of substrates or preforms that are to be densified simultaneously in order to increase the throughput of the densification method, and consequently to increase the load factors of reaction chambers.
Methods and installations for densifying porous annular substrates by chemical vapor infiltration are described in particular in documents: US 2004/237898 and U.S. Pat. No. 5,904,957. Nevertheless, those methods relate essentially to densifying substrates of annular shape arranged in stacks and they are not suitable for densifying substrates that present shapes that are not axisymmetric.
Document US 2008/0152803 describes using loader tooling comprising a tubular duct arranged between first and second plates and having thin substrates with the shape of the plate that is to be densified arranged radially therearound. The tooling as loaded in this way is then placed inside a reaction chamber of an infiltration oven having its reagent gas admission inlet connected to the tubular duct so as to enable a reagent gas to be admitted into the duct, which then distributes the gas along the main faces of the substrates in a flow direction that is essentially radial.
Nevertheless, that loader tooling remains limited to directed flow densification of substrates that are thin and simple in shape such as thin rectangular plates, and it does not make it possible to obtain uniform densification of substrates that are of complex three-dimensional shape such as fiber preforms for blades. The flow of a gas stream over substrates that are of complex three-dimensional shape is more difficult to control. The lack of control over the flow of the reagent gas over the set of substrates to be densified leads to the appearance of densification gradients in the substrates. However, it is the uniformity with which a substrate is densified that determines the mechanical performance of the resulting part.